In recent years, a dynamic range for images has been higher along with higher bits of an image sensor.
A dynamic range of an image can be generally expressed with a ratio between minimum luminance and maximum luminance.
A high dynamic range (HDR) image as known as high-quality image has a contrast ratio of 10000:1 or more between highest brightness and lowest brightness, for example, and can realistically express an actual world.
With a HDR image, almost all the luminance in a visible range can be recorded, and a dynamic range and color gamut equivalent to human visible characteristics can be supported. A HDR image can be a much higher-quality image than conventional images in terms of realistic expression of shading, expression of dazzle, and the like.
While content productions actively shoot and produce HDR images, many display apparatuses such as a home TV for watching or listening to contents cannot actually display the HDR images.
Many display apparatuses such as a home TV are standard dynamic range (SDR) display apparatuses capable of displaying images with a lower dynamic range than the HDR images. Actually, only some users utilize HDR-compliant display apparatuses with maximum luminance of 500 nit or 1000 nit.
In a case where a HDR image is input in and displayed on a SDR display apparatus, the original luminance information and color information of the HDR image are lost and an image with deteriorated image quality is displayed. Additionally, in a case where a HDR image is output as SDR image, a processing (also called display mapping) of adapting the dynamic range of the original contents to the SDR display apparatus to which the image is output may be performed (see Patent Document 1, for example)
However, all the display apparatuses do not include the display mapping function. Further, in a case where a dynamic range is simply converted by linear scaling, a large amount of information is lost, and there is a concern that the images in which appearances of humans are largely different before and after the conversion. The loss of information has an effect on an intention of a content production or supplier.